Process for dry sterilization of medical devices and materials

ABSTRACT

A process for dry sterilization of medical or dental devices and materials in which these materials are subjected to an electrical discharge in a gaseous atmosphere to produce an active low temperature plasma for surface sterilization and treatment of the devices and materials.

This is a Continuation-In-Part of U.S. patent application No. 072,899filed July 14, 1987, to be issued under U.S Pat. No. 4,818,488 on Apr.4, 1989 which is a Continuation-In-Part of U.S. patent application Ser.No. 019,134 filed Feb. 25, 1987, now issued to U.S. Pat. No. 4,801,427issued Jan. 31, 1989.

BACKGROUND OF THE INVENTION

Modern medical and dental practice require the use of aseptic materialsand devices, many of them meant for repeat use. In order to achieve thissterilization, processes are needed, at the manufacturer, and also atthe hospitals or dental offices for treatment of reusable materials anddevices.

Typical of materials which are reused in the hospital environment andrequire repeated sterilization are major surgical instrument trays,minor surgical kits, respiratory sets, fiber optics (endoscopes,proctoscopes, angioscopes, bronchioscopes) and breast pumps. Typicalinstruments and devices which are reused in a dental environment andrequire repeated sterilization are hand-pieces, dental mirrors, plastictips, model impressions and fabrics.

There are a wide variety of medical devices and materials that are to besupplied from the manufacturer already packaged and sterile. Many ofthese devices and materials are disposable. Typical of this group arebarrier packs, head coverups and gowns, gloves, sutures, syringes andcatheters.

One major sterilization process in present use is that which employsethylene oxide (EtO) gas in combination with Freon-12 (CCl₂ F₂) at up tothree atmospheres of pressure in a special shatter-proof sterilizationchamber. This process, in order to achieve effective asepsis levels,requires exposure of the materials to the gas for at least one to threehours followed by a minimum of twelve hours, or longer, aeration period.The initial gas exposure time is relatively long because thesterilization is effected by alkylation of amino groups in theproteinaceous structure of any microorganism. EtO sterilization requiresthe attachment of the entire EtO molecule, a polyatomic structurecontaining seven atoms to the protein. This is accompanied by therequirement of hydrogen atom rearrangement on the protein to enable theattachment of EtO. Because of kinetic space-hindrance factors governingthe attachment of such a bulky molecule, the process needs to be carriedout at high pressure and be extended over a long period of time. It is,therefore, deemed very inefficient by the industry at large.

Perhaps the chief drawback to this system, however, is its dangeroustoxicity. Ethylene-oxide (EtO) is a highly toxic material dangerous tohumans. It was recently declared a carcinogen as well as a mutagen. Itrequires a very thorough aeration process following the exposure of themedical materials to the gas in order to flush away toxic EtO residuesand other toxic liquid by-products like ethylene glycol and ethylenechlorohydrin. Unfortunately, it is a characteristic of the gas and theprocess that EtO and its toxic by-products tend to remain on the surfaceof the materials being treated. Accordingly, longer and longer flush(aeration) times are required in order to lower the levels of theseresidues absorbed on the surface of the materials to a safe operationalvalue. A typical volume for each batch using this EtO process is 0.2 to50 cu. ft. within the health and dental care environments.

A number of other approaches for performing sterilization have also beenemployed. One such process is high pressure steam autoclaving. However,this requires high temperature and is not suitable for materials whichare affected by either moisture or high temperature, e.g., corrodableand sharp-edged metals, plastic-made devices, etc., employed by thehospital and the dental communities.

Another approach utilizes either x-rays or radioactive sources. Thex-ray approach is difficult and expensive. The use of radioactivesources requires expensive waste disposal procedures, as well asrequiring radiation safety precautions. The radiation approach alsopresents problems because of radiation-induced molecular changes of somematerials, which, for example, may render flexible materials brittle,e.g., catheters.

It is therefore a primary object of the present invention to provide aprocess and apparatus for dry sterilization of medical and dentaldevices and materials, which can be operated efficiently, both withrespect to time and volume and which can be carried out below 70° C.

It is another object of the present invention to provide a safe,nontoxic, process for the sterilization and surface treatment of medicaland dental devices and materials, a process which does not employ toxicfeed gases and one which does not yield toxic absorbed surface residuesand by-products.

SUMMARY OF THE INVENTION

Broadly speaking in the present invention, sterilization or surfacetreatment is achieved by exposing the medical or dental devices andmaterials to a highly reducing gas plasma like that generated by gasdischarging molecular hydrogen, or to a highly oxidizing gas plasma, forexample, one containing oxygen. Depending on the specific sterilizationrequirements, a mildly oxidizing environment, somewhere between theenvironment offered by oxygen and that offered by hydrogen is presentedby gas discharging molecular nitrogen, either in pure state, or inmulticomponent mixtures with hydrogen or oxygen, supplemented by aninert gas. In such a manner, plasma discharge chemical-physicalparameters can be adjusted to fit almost any practical application ofsterilization and surface treatment.

Such a plasma is generated by creating an electrical discharge in agaseous atmosphere maintained at sub-atmospheric or atmosphericpressure, within which the materials to be sterilized are placed.

Generation of gas plasmas is a very well developed discipline, which hasbeen specifically employed in semiconductor processing. See, forexample, U.S. Pat. Nos. 3,951,709; 4,028,155; 4,353,777; 4,362,632;4,505,782 and Re. 30,505 assigned to the present inventor.

In one instance the gas plasma sterilization process of this inventioninvolves evacuating a chamber to a relatively low pressure after thedevices or materials to be sterilized or treated have been placed withinit.

An oxidizing gaseous atmosphere, as an example, is then provided to thechamber at a relatively low pressure, typically in the range 10 micronsHg to 10 torr, corresponding to a continuous gaseous flow rate range of20 to 3000 standard cc per minute. An electrical discharge is producedwithin the chamber by conventional means, such as a microwave cavity ora radio frequency (RF) excited electrode. Alternatively, RF power in thepower density range 0.0125-0.08 W/cm³ may be coupled into the gas via asingle electrode disposed within the chamber in a nonsymmetricalelectrical configuration, or via two electrodes contained within thechamber in an electrically symmetrical configuration. In either case thematerial to be sterilized is placed on one of the electrodes, while thechamber's wall is commonly maintained at ground potential.

The nonsymmetrical arrangement provides the basis for a low plasmapotential mode of operation which is conducive to low sterilizationtemperatures and the suppression of otherwise deleterious ionbombardment and contamination of the devices and materials.

The resultant discharge produces a gas plasma including both excitedelectrically charged gaseous species and excited electrically neutralgaseous species. For example, free radicals of atomic oxygen as well asexcited molecular oxygen are formed in a discharge through molecularoxygen. These oxygen-bearing active species interact chemically with theproteinaceous components of the microorganisms residing on the surfacesof medical or dental devices to be sterilized, thereby denaturing theproteinaceous molecules and achieving kill rates of microorganismsequivalent to a probability of microorganism survival of less than onein a million.

The efficiency of this process is due, in part, to the fact that thegaseous plasma entities are very reactive and atomically small (usuallymonoatomic or diatomic) and therefore exhibit an enhanced ability tochemically attach themselves to a proteinaceous structure and/orabstract (remove) hydrogen atoms from it. It was also ascertained thatthe presence of low levels of water vapor in the plasma feed gasenhances sterilization efficiency dramatically. It is believed thataccentuation of active species concentration and/or favorablepreconditioning of micro-organisms' proteinaceous structure occurs inthe presence of moisture during the discharge process. These processesare responsible for the total kill of the microorganisms. The kineticspace (or steric) restriction for this type of interaction is at leastone thousand times lower than that for EtO alkylation.

Several specific types of interaction take place. One specificinteraction is hydrogen abstraction from amino groups. Another isrupturing ring structures, particularly those including nitrogen, orcarbon-carbon bond cleavages. It is important to note that theseprocesses produce only gaseous effluents, such as water vapor and carbondioxide, which would not remain absorbed on the surface of medicaldevices, but would, instead, be carried away from such devices with themain gas stream to the pump.

This sterilization process may be used with pre-packaged materials, suchas disposable or reusable devices contained within gas-permable bags orpouches. With sealed pouches (e.g., polyethylene/Tyvek packaging), thebarrier wall of the package is pervious to the relatively small activespecies of the sterilizing plasma, but impervious to the largerproteinaceous microorganisms. (Tyvek is a bonded polyolefin produced byDuPont.)

After evacuation of the chamber, and introduction of the gas or gasmixture, the gas(es) will permeate the package wall with a dynamic freeexchange of gas(es) from within and from outside the package.

Upon striking a microwave or an RF discharge to form the plasma, and,depending upon electrical configuration and pressure, the plasma mayactually be created within and outside the package or, alternatively,the package may be placed in a substantially electrically shielded(field-free) glowless zone, so that it is subject to predominantlyelectrically neutral, rather than electrically charged, active specieswhich pass through the packaging wall to interact with the surface ofthe materials it contains.

In yet a different electrical configuration, the packages containingdevices to be sterilized can be placed on a conveyor belt and swept intoan atmospheric pressure corona discharge gap operated in ambient air.With this configuration, the discharge electrodes are comprised of agrounded metal-backed conveyor belt forming the bottom electrode, whilethe top electrode is comprised of a metal block with multipleneedle-like nozzles for the dispersion of gas into the discharge gap.

Sterilization with this continuous, in-line, apparatus, is brought aboutby either ozone formation, due to presence of discharged oxygen in air,or due to any other oxidizing gas mixture that can be introduced intothe discharge gap via a plurality of nozzles, which are an integral partof the top electrode.

This corona discharge will normally operate in the power density range5-15 W/cm² and in the frequency range 10-100 KHz and 13-27 MHz,associated with gas flows in the range of several standard liters persecond.

For example, in order to enable device sterilization by a stronglyoxidizing plasma when employing the process with a polyethylene-basedpackaging, it is necessary to provide that oxygen-bearing active speciescan permeate through the organic package barrier in the first place, andthat a sufficient number of these species traverse that barrier in orderto effectively kill all microorganisms on a medical or dental deviceenclosed within the pouch.

Relevant strongly reducing, oxidizing, mildy oxidizing or mildy reducingconditions can be obtained by plasma discharging diatomic gases likehydrogen, oxygen, nitrogen, halogens, or binary mixtures of oxygen andhydrogen, oxygen and nitrogen (e.g., air), oxygen and inert gases, orthe gaseous combination of oxygen, nitrogen and inert gases like heliumor argon, depending on the particular substances to be sterilized ortreated.

The predominance of oxygen in the above mixtures is preferred but notmandatory. A predominance of nitrogen, for example, will result inmildly oxidizing conditions, but in somewhat higher process temperaturesduring sterilization for a given reaction pressure and power density.The inert gas fraction can be variable in the range 10 to 95%; thehigher the fraction, the lower the processing temperature for a givenpressure and power density. However, sterilization exposure timeincreases the higher the inert gas fraction in the mix. Substitution ofargon for helium, for example, will result in higher sterilizationtemperatures for a given pressure and power density. In this case,instability of the gas discharge operation may set in, requiring a powerdensity increase at a given pressure, compared to that employed withhelium, resulting in higher process temperatures.

Effective sterilization can also be obtained with a pure reducinghydrogen plasma or with a plasma discharge through pure inert gases likefor example, helium, argon, and their mixtures, due to their very stronghydrogen atom abstraction (removal) capabilities from proteinaceousstructures of microorganisms. The addition of pure helium to an argonsterilizing plasma will enhance the stability of the latter and reduceoverall sterilization temperatures. Hydrogen and its mixtures witheither nitrogen or oxygen, or with both, in the presence or absence ofan inert gas, will show effective sterilization capabilities over a widerange of concentrations in these mixtures, thereby enhancingsterilization process flexibility and versatility.

A first objective of facilitating the gaseous permeation through anorganic barrier (e.g., plastic or paper) is accomplished by evacuatingthe chamber (containing the loaded pouches) to a base pressure ofapproximately 20 microns Hg. This rids the pouches of previouslyentrapped atmospheric air, and equalizes the pressure inside the pouchto that inside the chamber (across the organic barrier). The subsequentintroduction into the chamber of an oxygen-containing gas, in a typicalsituation, will establish an instantaneous higher pressure inside thechamber (outside the pouch) relative to that inside the pouch. Thispressure gradient across the pouches' barrier will serve as the initialdriving force of gas into the pouch. At an equilibrated state, an activeand ongoing interchange of molecules across the barrier will take place,attempting at all times to maintain the same pressure on both sides ofthe organic barrier. Upon striking a discharge through this gas,oxygen-bearing active species will be generated. Typically, these activespecies will be deactivated in large amounts by the organic barrier ordue to interaction with neighboring metallic surfaces. This willcommonly substantially reduce the availability of these active speciesto do the sterilizing job.

In order to accomplish the objective of generating a sufficient numberof reactive species traversing the organic barrier of a package toeffect efficient sterilization cycles, the plasma discharging of gaseousmoisture mixtures proved extremely beneficial. Plasma discharging ofvarious innocuous gases containing moisture levels in the range 100 to10,000 ppm of water vapor enabled the accentuation of active speciesconcentration by more than a factor of two, thereby substantiallyshortening sterilization exposure times. Consequently, in a few systemconfigurations which were previously characterized by relatively highprocessing temperatures, process temperatures were now kept sufficientlylow due to the shortened sterilization cycles. Effective binary moisturemixtures were those comprised of oxygen, nitrogen, hydrogen and argon.Ternary moisture mixtures of nitrogen-oxygen and argon-oxygen weresomewhat more effective at similar power densities than moisturemixtures of pure nitrogen or pure argon. Moisture mixtures containinghalogens although very effective, were too corrosive and toxic. The mosteffective moisture mixture was that of oxygen, reducing sterilizationcycles by more than a factor of two.

In addition, it was found that the organic barrier of a packaging pouchcould be passivated in such a way as to substantially reduce its take-upof oxygen-bearing active species needed as a sterilizing agent and onewhich must render a final non-toxic medical device, without theformation of any toxic by-products.

One such passivation method consists of simultaneously introducing intothe chamber a gaseous mixture, which in addition to oxygen-containinggas(es), also contains selected other gases as set forth below:

1. Organohalogens, based on carbon and/or silicon, attached to any ofthe known halogens. Particularly those organic compounds of carbonand/or silicon that are saturated or unsaturated and contain in theirmolecular structures one (1) or two (2) carbon or silicon atoms attachedto: a predominance of fluorine atoms; a predominance of chlorine atoms;a predominance of bromine or iodine atoms; an equal number of fluorineand chlorine atoms simultaneously; an equal number of chlorine andbromine atoms simultaneously; an equal number of fluorine and bromineatoms simultaneously; an equal number of fluorine and iodine atomssimultaneously; an equal number of chlorine and iodine atomssimultaneously. A predominance of fluorine in these compounds includesstructures where all other atoms attached to a carbon or a silicon atomcan be all the other halogens, or only one or two other halogens out ofthe four halogens known, in conjunction with other atoms, as for examplehydrogen. The same comments apply to a predominance of chlorine, bromineand iodine. For the latter, however, the simultaneous presence ofbromine is unlikely to be practical due to a low volatility of thestructure, but the simultaneous presence of fluorine or chlorine, orboth, is practical. It is worth noting that hydrogen-containingorganohalogens will have a tendency to polymerize under plasmaconditions, and in some cases, be flammable in as-received condition.

Most effective sterilizing mixtures of oxygen and an organohalogen arethose where the organohalogen is a mixture of organohalogens in itself,either based on carbon and/or silicon, where the oxygen fraction is over70% by volume; yet sterilization will be effected for lower oxygencontent at the expense of excessive halogenation of the surface of thematerial to be sterilized, and at the expense of excessive loss oftransparency of the wrapping pouch.

2. Organohalogens in conjunction with either nitrogen or an inert gaslike helium or argon. In these cases, it is considered practical to keepthe fraction of the inert gas in predominance in order to keep theprocess temperature as low as possible. Inert gas fractions up to 95% byvolume will be effective in killing microorganisms. The nitrogenfraction is ideally kept below that of the oxygen fraction.

3. Inorganic halogens, defined as compounds not containing carbon orsilicon, but preferably containing as the central atom or atoms eitherhydrogen, nitrogen, sulfur, boron, or phosphorus linked to any of theknown halogens in a similar manner as described for the organohalogensunder item 1 above, or defined as compounds that contain only halogenswithout a different central atom, like for example molecular halogens(e.g., F₂, Cl₂) and the interhalogens which contain two dissimilarhalogen atoms (e.g., Cl-F, I-F, Br-Cl based compounds, etc.). Also inthis case the inorganic halogen maybe, in itself, a mixture of differentinorganic halogens as defined above.

Most effective sterilizing mixtures of oxygen and an inorganic halogenare those where the oxygen fraction is over 80% by volume; yetsterilization will be effected for lower oxygen content at the expenseof excessive halogenation of the surface of the material to besterilized, and at the expense of excessive loss of transparency of thewrapping pouch.

4. Inorganic halogens in conjunction with either nitrogen or an inertgas as described in item 2 above.

5. Inorganic oxyhalogenated compounds, not containing carbon or silicon,but preferably contain either nitrogen, phosphorus, or sulfur, each ofwhich is simultaneously attached to oxygen and a halogen (e.g., NOCl,SOCl₂, POCl₃, etc.). More specifically, the nitrogen-oxygen, or thesulfur-oxygen, or the phosphorus-oxygen entities in the previousexamples are linked to any of the known halogens in a similar manner asdescribed for the organohalogens under item 1 above. The inorganicoxyhalogenated fraction may be, in itself, a mixture of differentinorganic oxyhalogenated compounds as defined above.

Most effective sterilizing mixtures of oxygen and an inorganicoxyhalogenated structure are those where the oxygen fraction is over 70%by volume; yet effective sterilization will be obtained for lower oxygencontent at the expense of excessive halogenation of the surface to besterilized, and at the expense of excessive loss of transparency of thewrapping pouch.

6. Inorganic oxyhalogenated compounds in conjunction with free nitrogenor an inert gas as described in item 2 above.

7. Multicomponent mixtures comprised of members in each of theaforementioned groups. The simultaneous presence of free nitrogen and aninert gas like helium or argon in any of the above mentioned groups, orin multicomponent mixtures comprised of members in each of theaforementioned groups, will also be effective in killing microorganisms.The free nitrogen fraction should be ideally below that of oxygen inorder to maintain a lower reaction temperature.

More specific and relatively simple multicomponent mixtures that areeffective sterilants as well as effective organic barrier passivationagents are listed below:

    ______________________________________                                        Specific Multicomponent Mixtures Comprised of                                 Fractions A + B (percent of fraction is by volume)                            Fraction A           Fraction B                                               ______________________________________                                        O.sub.2 (92-97%)     CF.sub.4 (3-8%)                                          [O.sub.2 (40%)--He(60%)]                                                                           CF.sub.4 (0.25-3%)                                       [O.sub.2 (8%)--CF.sub.4 (92%)]                                                                     He(80%)                                                  [O.sub.2 (17%)--CF.sub.4 (83%)]                                                                    He(80%)                                                  [O.sub.2 (83%)--CF.sub.4 (17%)]                                                                    He(80%)                                                  [O.sub.2 (92%)--CF.sub.4 (8%)]                                                                     He(80%)                                                  ______________________________________                                    

Many of the aforementioned gas mixtures are, in themselves, novelchemical compositions.

The plasma discharge through such a composite mixture will, for example,create both oxygen-bearing and fluorine, or chlorine-bearing activespecies simultaneously. The latter will predominantly be responsible forpassivating the organic barrier, since fluorination or chlorination,rather than oxidation of the organic barrier is favoredthermodynamically. Therefore, the take-up of fluorine orchlorine-bearing active species by the organic barrier of the pouch willbe preferential. This will leave a relatively larger fraction ofoxygen-bearing active species available for sterilization, since thelatter cannot easily be taken up by a fluorinated or chlorinatedsurface.

In addition, sterilization by oxygen-bearing active species may beaided, for example, by simultaneously discharging an oxygen-containingand fluorine or chlorine containing gas residing inside the enclosingpouch. This gas had previously permeated through the organic barrierprior to the commencement of the discharge. This will create activespecies that contain both oxygen and fluorine or chlorine within thepouch directly. As previously described, the competition for take-up bythe organic barrier (pouch) will be won by the fluorinating orchlorinating species, leaving a larger net concentration of activespecies containing oxygen to do an effective sterilizing job.

However, residual fluorine or chlorine-bearing active species within thepouch and not taken-up by it will also perform effective surfacesterilization, since they are strongly chemically oxidizng agents. But,the fraction of fluorine or chlorine-containing gas in the originalcomposite gaseous mixture, is substantially smaller than theoxygen-containing component. Thus, a major portion of microorganismskill will be attributed to the oxygen-bearing species in the plasma. Ineither case, however, the end result is a continuous attack on theproteinaceous structure of the microorganism resulting in itsdegradation and fragmentation into gaseous products. This chemicalaction by the reactive plasma is to initially modify (denature) theproteinaceous network of the microorganism, disrupting its metabolism ata minimum, but more commonly impeding its reproduction.

DESCRIPTION OF THE DRAWINGS

In the drawing FIG. 1 is a general diagrammatic illustration of anapparatus suitable for use in the practice of this invention;

FIG. 2 is a cross sectional view of another apparatus suitable for usein the practice of this invention;

FIG. 3 is a generally diagrammatic illustration of another apparatussuitable for use in the practice of this invention;

FIG. 4 is a cross sectional view of another embodiment of asterilization chamber for use in the practice of the invention;

FIG. 5 is a side view of the apparatus of FIG. 4; and

FIGS. 6, 7, 8, 9, 10, 11, 12, 13 and 14 are cross sectional and sideviews of alternative embodiments.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a general diagrammatic illustration of an RF excited dischargechamber of the type used in the process of this invention. Thecylindrical chamber 11 is formed, in this instance, of glass or quartzand encloses within it the material 14 to be treated. The chamber iscommonly connected to a mechanical vacuum pump (not shown) thatestablishes sub-atmospheric pressure conditions within the chamber. Anexciter coil 12 couples RF energy from RF source 13 to the gas enclosedwithin the gas tight chamber creating a plasma therein.

Alternatively, a microwave discharge cavity operating at 2450 MHz mayreplace the RF exciter coil to couple power into the gas. With asuitable selection of a reducing gas, like hydrogen, or an oxidizinggas, such as oxygen, as a typical example, a discharge may be initiatedand maintained within the chamber. In the gas plasma formed by such adischarge a number of excited species, both molecular and atomic, areformed. The interaction of these species with a surface of the device ormaterial to be sterilized accomplishes the sterilization in the mannerdescribed above. The time duration of the process needed to achievesatisfactory sterilization will vary with other parameters of thedischarge such as gas flow, pressure, RF or microwave power density, andload size.

In the embodiment illustrated in FIG. 1 the apparatus includes an innerperforated metallic cylinder 15 mounted generally concentric with thelong axis of the chamber 11, to form within the perforated cylinder asubstantially glowless, field-free zone. The perforated cylinder 15 iselectrically-floating and is cooled by recirculating a suitable coolant(e.g., a 50-50 mixture of water and ethylene glycol) through coolingcoils 9 wrapped around the cylinder's length, to effect lowsterilization temperatures (<70° C.) Still lower sterilizationtemperatures could be effected with two concentric perforated metalliccylinders 15 and 15a, surrounded by cooling coils 9 and 8, respectively,and enclosed by non-conducting chamber 11, as shown in FIG. 2. Energycoupling into this chamber is accomplished in a similar manner asdescribed in FIG. 1. In a few cases, the configurations described inFIGS. 1 and 2 may not require cooling coils 8 and 9 if the plasma feedgas contains low levels of water vapor for the enhancement ofsterilization efficiency and the reduction of processing cycle time andtemperature.

The resultant glowless and field-free zone within the confines of theelectrically floating perforated cylinders could be ascribed toelectrical faraday-cage effects, coupled with catalytic deactivation ofactive species, which are the precursors of visible emission, on themetallic surface of the perforated cylinder.

When, as illustrated in FIG. 3, a microwave energy source 18 at forexample, 2540 MHz. is employed in lieu of the RF generator 13, theperforated metallic cylinder cannot be mounted concentric about the longaxis of the chamber. Instead, the microwave cavity 16 is mounted at oneend of a metallic or non-metallic chamber 11, and a perforated metallicshield 17 cooled by coolant-recirculating coils 20 may be placed justbeyond it toward the opposite end of the chamber, spanning the entirediameter cross section of the chamber, thus creating a field-free andglowless reactive zone immediately below it and away from the microwavecavity. These arrangements permit material 14 placed within this zone tobe generally isolated from electrically charged species, while allowingthe electrically neutral reactive plasma species, such as, for example,oxygen radicals, to interact with the surface of the material to besterilized. In this manner, sterilization is commonly effected atsubstantially lower process temperatures.

Alternatively, the perforated metallic shield 17 may be removed, ifmicrowave cavity 16 is remotely located from material 14.

Microwave discharges lend themselves to this mode of operation, sincethe effectiveness of neutral active species generated in such adischarge survive substantial distances downstream, and away from, themicrowave cavity itself. This is a direct consequence of the higherpopulation of electrons in microwave plasmas, and consequently thehigher degree of ionization and dissociation in these discharges. Also,microwave plasma electric probe measurements indicated plasma potentialsnearly equal to ground potential, thereby practically eliminatingenergic particle bombardment during processing. This mode of operationis thus well suited for low temperature exposure of heat-sensitivedevices and material, even for extended periods of sterilization time.

In the most preferred embodiments, the chamber is formed of a metallicelectrically grounded and water-cooled outer shell with either a singleinternal perforated cylindrical shield, as shown in FIG. 1, or perhapswith two such metallic shields, as shown in FIG. 2, which may be alsopurposely cooled, the RF energy being coupled, in this latterconfiguration, between the two conducting perforated cylinders. Ineither case, conditions for low plasma potentials will prevail, with thedischarge glow being confined to the space between the inner wall of thechamber and the surface(s) of the perforated cylinder(s), leaving thework volume defined by the inner perforated cylinder substantially,field-free, void of the plasma glow, and at a relatively low operatingtemperature.

One such chamber configuration is illustrated in FIGS. 4 and 5. Thecylindrical outer wall 21, typically formed of aluminum cr stainlesssteel, is maintained at ground potential and serves as the chamberenclosure. This enclosure may be water-cooled with the aid of coolingcoils 28 wrapped around it. Suitable dimensions for this chamber are adiameter of 36" and a length of 48". A metallic perforated innercylinder 23 cooled by cooling coils 19 is mounted on insulating spacers29 within the chamber so that it is positioned generally parallel withthe long axis of the outer wall 21 of the chamber and concentric withit. These spacers may be formed of any suitable non-reactive andinsulating type of material such as ceramic. The cylinder perforationsare typically 2.5-4 mm diameter holes spaced in all directions from oneanother by approximately 0.5 cm in a triangulated manner. Longitudinalsupport rails 27 are fastened to the inner wall of the perforatedcylinder 23 to support a wire basket 25 in which the materials anddevices to be sterilized are placed. A suitable RF source 22 is coupledbetween the grounded outer chamber wall 21 and the perforated innercylinder 23. Usually this RF source should be capable of producing an RFoutput in the range 0.01 to 0.1 W/cm³ at frequencies in the 10-100kilohertz or 13-27 megahertz range.

As illustrated in FIG. 5, an evacuation port 31 at the end of cylinder21 is connected to a pump (not shown) and provides for suitableevacuation of the chamber and for continuous gas flow during thesterilization process. The gas supplied for the discharge is generallyflowed through the chamber by means of perforated diffusion tubes 35.Alternately, gas may be introduced into the chamber via a gas dispersiondevice (not shown) mounted behind chamber door 39 from the inside.

Material to be sterilized may be placed within wire basket 25 resting onrail 27 through the entry port behind chamber door 39. Chamber door 39may be any suitable closure that can be conveniently opened and closedand left in a sealed position during evacuation and the gas dischargeoperation.

FIG. 6 illustrates a second preferred embodiment of the apparatus forpracticing the process of the invention. In this configuration, theouter chamber wall 21 may be water-cooled by cooling coils 28, is againformed of metal, such as electrically grounded aluminum or stainlesssteel, and is of similar dimensions to that illustrated in FIG. 4.Mounted within the chamber is an inner concentric cylinder 43 formed ofa perforated metal which may be purposely cooled by cooling coils 30,and is supported on insulating support struts 46. The spacing betweenthe inner wall of the chamber and the perforated interior cylinder mayrange typically from 10 to 17 cm, where the chamber has an I.D. of 36".A second metallic perforated cylinder 41 is concentrically mountedintermediate between the inner perforated cylinder 43 and the inner wallof the chamber and may also be cooled by cooling coils 19. This secondperforated cylinder is supported on insulating struts 47 and is spacedtypically 4 to 7 cm away from the inner perforated cylinder 43. Theinsulator struts may again be formed of a ceramic material. Mounted onthe interior of the inner concentric cylinder 43 are support rails 27for carrying a wire basket which would contain the materials to besterilized. Both the outer chamber wall 21 and the inner perforatedcylinder 43 are electrically connected to point of potential reference(ground). Electrical connections would most usually be made throughceramic seal feedthroughs 48 and 49. The intermediate cylinder 41 iselectrically connected to one side of the RF power supply 22, the otherside of which is connected to the point of potential reference.

While a variety of conventional RF sources may be used, the most typicalvalue for the RF frequency is 13.56 MHz or, alternatively, 10-100 KHz.As in the embodiment of FIG. 5 longitudinally extending gas diffusiontubes 35 may be employed to provide the gas to the interior of thechamber. Typically each tube would have holes of diameter between 0.5and 1.5 mm, spaced approximately 1" apart along its length. The holediameters closer to the gas source would be of the smaller diameter.Alternatively, gas inlets may be provided behind chamber door 39. Asindicated in the embodiments of FIGS. 4, 5 and 6 the perforated innercylinders may be open-ended at both ends or, may be closed with the sameperforated stock as is used to form the cylinder(s). The sterilizationchambers shown in FIGS. 4, 5 and 6 may be connected to a microwavedischarge source, typically operating at 2540 MHz, in lieu of an RFenergy source. In this case, the concentric perforated metalliccylinder(s) may be replaced by a single perforated shield in accordancewith the operational description given for FIG. 3.

FIG. 7 illustrates a third preferred embodiment of the apparatus forpracticing the process of the invention. In this diagrammaticdescription the outer chamber wall 21 is again formed of metal, such asaluminum or stainless steel, and is of similar dimensions to thatillustrated in FIG. 4. Mounted within the chamber are two planar,metallic, electrodes 50 and 51, preferably constructed of aluminum whichmay be coated with insulating aluminum oxide. The gap 52 betweenelectrodes 50 and 51, is adjustable by virtue of the movable bottomelectrode 50. Terminals A and B are connected to the electrodes via aninsulating feedthrough 48. The outer end of these terminals may beconnected to an RF source (not shown) in such a way that when terminal Bis connected to a ground potential, terminal A must be connected to theRF source, or vice versa, providing for an electrical symmetricalconfiguration. The work load to be sterilized is placed on lowerelectrode 50.

It is important to maintain the distance between the electrodes alwayssmaller than the distance of the RF-powered electrode's edge to thegrounded chamber's wall. This enables a well defined and intense plasmaglow to be confined to space 52 between the electrodes and preventsdeleterious sparking. The electrode material may also be made of theperforated stock previously mentioned. However, it is desirable to havethe RF-powered electrode made of solid stock to enable very efficientwater-cooling of that electrode. The bottom electrode may also be madeof solid stock to enable a cooler surface upon which the work load to besterilized will be placed. This chamber will commonly be evacuated to10-100 microns Hg before gas introduction via the perforated gasdiffusion tubes 35. Practical device sterilization can be obtained withprocess parameters for gas flow rates in the range 20 to 3000 scc/m,corresponding to a total sterilization reaction pressure of 10-5000microns Hg, at a range of RF power densities of 0.0125 to 0.08 W/cm³.Process exposure times will depend on load size and are commonly in therange 2 to 120 min.

FIG. 8 illustrates in diagrammatic form yet another preferred embodimentfor practicing the process of the invention. The outer wall of chamber21 is again formed of metal, such as aluminum or stainless steelmaintained at ground potential, and is of similar dimensions to thatillustrated in FIG. 4. Mounted within the chamber is a single planar,metallic, electrode 50, preferably constructed of aluminum which may becoated with insulating aluminum oxide to reduce RF sputtering. Thiselectrode is commonly connected to an RF source in the MHz range andcarries the work load to be sterilized. This electrode has commonly atotal surface area which is at least four times smaller than the totalinternal surface area of the grounded chamber, to effect a low plasmapotential mode of operation. This arrangement, coupled with low powerdensities (see below) is conducive to very low sterilizationtemperatures.

This electrical configuration is usually referred to as asymmetric andis conducive to generating an extremely uniform plasma glow filling theentire volume of the processing chamber. It is also responsible for thedevelopment of a characteristic accelerating potential at the surface ofelectrode 50, associated with a thin "dark space" through which positiveplasma ions will accelerate and impinge on the electrode and the workload it normally carries.

This arrangement is recommended for hard-to-sterilize materials almostexclusively, particularly for sterilization of metallic devices repletewith a high density of cracks and cravices.

The main advantage of this process chamber configuration is its abilityto render efficient sterilization at relatively low power densities inthe range of 0.0125-0.025 W/cm³. This configuration is also easilyscalable as a function of work load size.

This process chamber commonly operates with at least an order ofmagnitude lower pressure than the pressure for chambers described inFIGS. 1 through 7, while the gas dispersion tubes 35 are similar inconstruction to those previously mentioned. To prevent RF sputtering ofelectrode 50 due to positive ion bombardment, it may either behard-anodized or alternatively aluminum oxide spray-coated.

One particular sub-configuration to that described in FIG. 8 isillustrated in FIG. 9. In this configuration chamber 21 is water-cooledby cooling coils 28 and contains a perforated metallic enclosure 71totally surrounding and containing electrode 70. This enclosure may becooled by to a separate RF source 22a, of a different frequency thanthat of source 22. This perforated enclosure may be equipped with anopen/close hinging mechanism (not shown) to enable access for materialto be sterilized to be placed on electrode 70 contained within enclosure71. This yields the beneficial effect of being able to separatelycontrol the abundance of sterilizing active species and their impingingenergy. RF power applied to electrode 70, which may or may not include anegative DC potential from a separate DC supply, (not shown), willcontrol energy of ion impingement, while RF power applied to theauxiliary perforated enclosure 71, will control active speciesabundance.

With this configuration, RF power sources operating at 100 KHz and 13.56MHz may be used in the various possible permutations. Interestingresults are obtained by mixing both frequencies while being applied to asingle element. Commonly, one frequency has to be applied at a higherpower fraction, usually around 90% of the total applied power to thesame element. Such interesting process results were obtained when thetwo different frequencies were mixed and applied to electrode 70 in theabsence of any auxiliary perforated enclosure. The mixed frequencyconcept also lends itself to low power density sterilization in therange 0.0125 to 0.025 W/cm³, with the advantage of maintaining theoverall temperature relatively low (below 50° C.), particularly whenelectrode 70 is water-cooled by cooling coils 74.

It is worth noting that the auxiliary perforated enclosure 71 ought tobe of high mesh transparency to allow the plasma glow to extend past itand contact electrode 70. Best operating conditions will be obtained forthe smallest surface area of this perforated metallic enclosure. In afew instances, this metallic enclosure was connected to ground, yieldingeffective sterilization data.

FIG. 10 illustrates diagrammatically a preferred embodiment forpracticing the process of the invention under atmospheric pressureconditions in ambient air. In this configuration no vacuum capability isrequired. Material to be sterilized is placed on grounded andwater-cooled conveyor belt 62 which sweeps the load across the dischargegap created between conveyor belt 62 and RF-powered and water-cooledelectrode 61. Electrode 61 cooled by cooling coil 76 produces a largeplurality of needle-like discharges which create individual dischargesparks toward the counter grounded electrode 62. The larger the gapbetween the electrodes, the higher the power needed to initiate thedischarge in air.

Sterilization is effected due to ozone formation following the dischargeof oxygen in the ambient air. Power density requirements in the range 5to 15 W/cm² are not uncommon. Maintaining a controlled relative humidityof 50 to 60% in the discharge gap will facilitate initiation of thedischarge and promote atomic oxygen generation. The latter serves as aprecursor to ozone formation, the final desired sterilant in thisconfiguration.

Ozone toxicity inhibits wide acceptance of such a corona discharge inair for the purpose of medical or dental device sterilization.Alternatively, therefore, the RF-powered electrode 61 may assume aconfiguration comprised of multiple open nozzles 65, capable ofdispersing oxidizing gases immediately adjacent to conveyor belt 62. Inthis configuration the discharge would still be created in ambient air,however the dispersion through the open-nozzles 65 of a judiciouslyselected feed gas will increase the local concentration of its activespecies 63 relative to that of ozone. In this manner, sterilizationwould be attributable to active species derived from any feed gasintroduced into the hollow RF-powered electrode 61 and not to thedeleterious ozone gas.

The dispersing nozzles 65 may assume different configurations. Forexample, separate nozzle tubes may be inserted into a hollow section ofelectrode block 61, which may or may not be of different material thanelectrode block 61. These tubes may also be screwed into the electrodeblock 61 for easy replacement. A typical hole size for each individualnozzle is in the range 0.015-0.040".

The advantages of this discharge configuration are mainly in terms ofsystem simplicity and in the context of continuous operation, coupledwith the ability to easily change the residence time of a work loadwithin the discharge gap.

Disadvantages are commonly associated with erosion and degradation ofboth electrodes 61 and 62. Electrode 61 should be constructed fromoxidation-resistant materials (e.g., tungsten, molybdenum or alloysthereof). The grounded conveyor belt electrode 62 may be constructedfrom stainless steel or any other suitable nickel-coated metal, and maybe cooled by cooling coil 77. Alternatively, a dielectric conveyor beltmay be used. With such an arrangement, the insulating belt is mounted inclose proximity to a stationery grounded and fluid cooled metallic blockserving as the counter electrode. The conveyor belt ought to beresistant to electrical punch-through and be constructed fromfluorinated, fluorinated/chlorinated or fluorinated/chlorinatednitrogen-containing hydrocarbons (e.g., DuPont products). High meltingpolyimides or Kalrez-like synthetics may serve as alternate constructionmaterials for the conveyor belt. Kalrez is a polyimide manufactured byDuPont.

Other configurations are illustrated in FIGS. 11, 12, 13 and 14. Theseconfigurations are preferred embodiments for practicing the process ofthe invention with narrow bore and elongated tubulation, almostexclusively. They are particularly designated for the treatment andsterilization of fiber optics-based tubulations as, for example,endoscopes, proctoscopes, angioscopes or bronchioscopes, having internaldiameters as small as 2 mm and an overall length of about 1000 mm.

The outer wall of elongated chamber 91 is made preferentially ofnon-metallic material (e.g., glass, ceramic) but, may also be comprisedof a metallic/non-metallic structure. The chamber has a minimum internaldiameter of one and one half times that of the outside diameter ofelongated tubulation 94. The inner and outer surfaces of narrow boretubulation 94 need to be treated or sterilized. Both ends of narrow andelongated chamber 91 are hermetically plugged with gas permeable butmicroorganism-impervious membranes 99 (e.g., Tyvek). This arrangementensures the dynamic flow of an active plasma through and over tubulation94, and also secures its aseptic condition after sterilization andduring prolonged storage.

To effect sterilization or treatment of the inner and outer surfaces oftubulation 94, it is inserted into chamber 91 either bare or sealedwithin a gas permeable elongated pouch. The chamber is then plugged atboth ends with membranes 99.

The chamber is subsequently inserted into exciter coil 92 (FIG. 11)whose terminals are connected to a suitable RF energy source like theone described with respect to FIG. 1.

In another arrangement, the chamber may be inserted within the air gapof capacitive plates 93 (FIG. 12) whose terminals are connected to asuitable RF energy source like the one described with respect to FIG. 1.

Alternatively, chamber 91 may be brought into close proximity tomicrowave cavity 16 (FIG. 13) whose terminal is connected to a suitablemicrowave energy source as described with reference to FIG. 3.

In cases where the chamber is a metallic-non-metallic structure, thevarious energy sources described in FIGS. 11, 12 and 13 are coupled tothe chamber via the non-metallic portion of the chamber.

In each of the configurations of FIGS. 11, 12 and 13, one end ofelongated chamber 91 is temporarily vaccum-flanged to a gas delivery andmonitoring system (not shown), while the other free end of the chamberis temporarily vacuum-flanged to a gas exhaust pumping system (notshown).

At the end of the sterilization or treatment cycle, the gas flow and theenergy source are turned off, chamber 91 is disengaged from the powersource and from both vacuum flanges and stored for future use of narrowbore tubulation 94.

For practical reasons, a plurality of chambers 91 may be employed in aparallel electrical arrangement simultaneously, either in an RF ormicrowave discharge hook-up.

Chamber 91 may have a cooling jacket 95 around it as, for example, shownin FIG. 14. It is not mandatory that exciter coil 92 (FIG. 11) orcapacitive plates 93 (FIG. 12) enclose or extend over the entire lengthof tubulation 94; the latter may be partially contained or not containedat all within coil 92 or capacitor plates 93.

Set forth below are specific examples of suitable operating parametersfor effective sterilization employing various apparatus as illustratedin the figures. The particular chamber and corresponding configuration,are referenced in the examples. However, for each of the examples thegeneral technique involved was one in which the material to besterilized was placed directly in the reaction chamber, or placed withina Tyvek/polyethylene pouch which itself was sealed and placed in a wirebasket within the reaction chamber.

The materials used for verification of sterilization effectiveness were"Attest" vials obtained from 3M Company, or "Spordex" bacterial teststrips obtained from the American Sterilizer Company, each vial or"Spordex" envelope contained a bacterial strip having an original sporepopulation of not less than 1×10⁶ Bacillus Subtilis var Niger per strip,but more commonly in the range 2.2-4.0×10⁶ spores/strip. The stripscontained the permeable plastic vials were not brought into contact withthe culture solution contained in any of the vials prior tosterilization. The vials were placed within the Tyvek/polyethylene bagsduring the plasma sterilization, alongside devices or instruments to besterilized. The bags were always sealed during the sterilizationprocess.

For each example the chamber was first evacuated to an initial lowpressure level after the materials (in the bags or pouches) were placedwithin it. The chamber was thereafter filled with the appropriate gasprior to striking the discharge, and the gas continued to flow throughthe chamber at a controlled rate to establish a steady statesterilization pressure. The discharge was initiated by the applicationof RF or microwave power as indicated. The discharge was maintained fora controlled time period at the end of which the power was turned off,the chamber was first evacuated, then backfilled with air through abacteria retentive filter, and later opened and the samples removed. Thetemperature within the chamber during the process was maintained at lessthan 70° C., and more typically around 25° C. to 65° C., as sensed by aniron-constantan, type "J", thermocouple circuitry and monitored by ananalog temperature meter.

Subsequent to the tests, the spore strips in the "Attest" vials wherebrought into contact with the self-contained culture solution andincubated for 72 hr, at the end of which period microorganism growth orno growth would be indicated by the resultant color of the culturesolution. Alternatively, the spore strips were submitted to anindependent testing laboratory which performed a total plate count onthe sample strips using a procedure in which 100 milliliters of steriledeionized water were added to each strip in a sterile whirl-pak bag. Thebag was then placed in a lab blender for 10 minutes. One 10 milliliteraliquot of sample, a duplicate one milliliter sample, and twoconsecutive 10⁻¹ dilutions were plated using Tryptic Soy Agar. Theplates were then incubated at 30°-35° C. for 72 hours. After incubation,the plates were read and recorded, and the results calculated on aColony Forming Unit (CFU) basis.

EXAMPLE 1

With metal chamber and internal uncooled perforated cylinder, (FIG. 4)

Gas: O₂ (Pure)

Flowrate: 20 scc/min

Pressure: 0.30 torr

Power Density: 0.050 W/cm

Exposure time: 60 min.

Temperature: 66° C.

Resultant microbial count: <10 CFU (below sensitivity limit of countingtechnique)

Percent kill: 99.9999%

Metal chamber dimensions: 8"D×8"L

EXAMPLE 2

With metal chamber and internal cooled perforated cylinder, (FIG. 4)

Gas: O₂ (Pure)

Flowrate: 20 scc/min

Pressure: 0.30 torr

Power Density: 0.050 W/cm³

Exposure time: 60 min.

Temperature: 32° C.

Percent kill: Total kill

Metal chamber dimensions: 8"D×8"L

EXAMPLE 3

With Pyrex chamber and internal cooled perforated cylinder, (FIG. 1)

Gas: O₂ /CF₄ (8%)

Flowrate: 36 scc/min

Pressure: 0.35 torr

Power Density: 0.050 W/cm³

Exposure time: 60 min.

Temperature: 34° C.

Resultant microbial count: <10 CFU (below the sensitivity limit ofcounting technique)

Percent kill: 99.9999%

Pyrex chamber dimensions: 8"D×8"L

EXAMPLE 4

With metal chamber and two uncooled internal perforated cylinders, (FIG.6)

Gas: O₂

Flowrate: 20 scc/min

Pressure: 0.30 torr

Power Density: 0.050 W/cm

Exposure time: 60 min.

Temperature: 76° C.

Percent kill: Total kill

Metal chamber dimensions: 8"D×8"L

EXAMPLE 5

With metal chamber and two cooled internal perforated cylinders, (FIG.6)

Gas: O₂

Flowrate: 20 scc/min

Pressure: 0.30 torr

Power Density: 0.050 W/cm³

Exposure time: 60 min.

Temperature: 36° C.

Resultant microbial count: <10 CFU

Percent kill: 99.9999%

Metal chamber dimensions: 8"D×8"L

EXAMPLE 6

With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1)

Gas: He(59.85%)--O₂ (39.90%)--CF₄ (0.25%)

Flowrate: 48 scc/min

Pressure: 0.35 torr

Power Density: 0.050 W/cm³

Exposure time: 60 min.

Temperature: 31° C.

Resultant microbial count: <10 CFU

Percent kill: 99.9999%

Pyrex chamber dimensions: 8"D×8"L

EXAMPLE 7

With metal chamber and two cooled internal perforated cylinders, (FIG.6)

Gas: O₂ (60%)--He(40%)

Flowrate: (total) 42 scc/min

Pressure: 0.35 torr

Power Density: 0.050 W/cm³

Exposure time: 60 min.

Temperature: 32° C.

Resultant microbial count: <10 CFU

Percent kill: 99.9999%

Metal chamber dimensions: 8"D×8"L

EXAMPLE 8

With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1)

Gas: O₂ (pure)

Flowrate: 25 scc/min

Pressure: 0.30 torr

Power Density: 0.015 W/cm³

Exposure time: 30 min.

Temperature: 26° C.

Percent kill: Total kill

Pyrex chamber dimensions: 8"D×8"L

EXAMPLE 9

With Pyrex chamber and uncooled internal perforated cylinder, (FIG. 1)

Gas: O₂ (pure)

Flowrate: 25 scc/min

Pressure: 0.30 torr

Power Density: 0.015 W/cm³

Exposure time: 30 min.

Temperature: 83° C.

Percent kill: Total kill

Pyrex chamber dimensions: 8"D×8"L

For the following examples, the initial spore population was 4×10⁶spores/strip.

EXAMPLE 10

With microwave discharge and internal perforated metallic shield disc,(FIG. 3)

Gas: Helium/Argon (50%/50%, v/v)

Flowrate (total): 80 scc/min

Pressure: 0.40 torr

Power Density: 0.015 W/cm³

Exposure Time: 90 min

Temperature: 29° C.

Resultant Microbial Count: 1.7×10² CFUs

Percent Kill: 99.9993%

Pyrex chamber dimensions: 6"D×10"L

EXAMPLE 11

With microwave discharge and internal perforated metallic shield disc,(FIG. 3)

Gas: Oxygen (Pure)

Power Density: 0.015 W/cm³

    ______________________________________                                                                   Resultant                                          FlowRate                                                                              Pressure  Exposure Microbial  Percent                                 (scc/min)                                                                             (torr)    (min)    Count (CFUs)                                                                             Kill (%)                                ______________________________________                                        30      0.20      20       5.8 × 10.sup.5                                                                     77.6923                                 30*     0.22      45       <10        99.9999                                 ______________________________________                                         Temperature: 24-30° C.                                                 *Sample enclosed in barrier cloth, 2ply, American Textiles, Inc.         

Pyrex chamber dimensions: 6"D×10"L

EXAMPLE 12

With Pyrex chamber and two uncooled internal perforated cylinders, (FIG.1)

Gas: O₂

Flowrate: 70 scc/min

Pressure: 0.275 torr

Power Density: 0.016 W/cc³

Exposure Time: 45 min

Temperature: 92° C.

Percent Kill: Total Kill

Pyrex chamber dimensions: 9"D×13"L

Sample was the standard sterilization test pack provided by guidelinesof the Association for the Advancement of Medical Instrumentation (AAMI)

EXAMPLE 13

With Pyrex chamber and two cooled internal perforated cylinders, (FIG.1)

Same experimental conditions as in Example 12

Temperature: 54° C.

Percent Kill: Total Kill

Sterilization test pack employed was according to AAMI guidelines.

EXAMPLE 14

With Pyrex chamber and uncooled internal perforated cylinder

Gas: O₂

Flowrate: 70 scc/min

Pressure: 0.275 torr

Power Density: 0.014 W/cc³

Exposure Time: 30 min

Temperature: 85° C.

Percent Kill: Total Kill

Pyrex chamber dimensions: 9"D×13"L

EXAMPLE 15

With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1)

Same experimental conditions as in Example 14

Temperature: 47° C.

Percent Kill: Total Kill

Pyrex chamber dimensions: 9"D×13"L

EXAMPLE 16

With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1)

Same experimental conditions as in Example 14

Exposure time: 21/4 hr.

Temperature: 51° C.

Percent Kill: Total Kill

Pyrex chamber dimensions: 9"D×13"L

EXAMPLE 17

With Pyrex chamber and uncooled internal perforated cylinder

Gas: O₂ (containing 500 ppm of H₂ O)

Flowrate: 70 scc/min

Pressure: 0.275 torr

Power Density: 0.015 W/cc³

Exposure Time: 20 min.

Temperature: 61° C.

Percent Kill: Total Kill

Pyrex Chamber Dimensions: 9"D×13"L

EXAMPLE 18

With Pyrex chamber (9"D×13"L) and cooled internal perforated metalliccylinder, (FIG. 1)

Gas: Dry and moist Oxygen, Nitrogen and Argon (H₂ O level: 300 ppm)

Flowrate: 100 scc/min

Pressure: 0.280-0.300 torr

RF Power Density: 0.020 W/cc³

Temperature: 38°-57° C.

Sample Size per Experiment: Ten (10) 3M "Attest" vials with 4×10⁶spores/strip in each vial, placed in a sealed Tyvek/polyethylene pouch.

    ______________________________________                                        Exposure                                                                      Time (min)                                                                    ______________________________________                                                   Dry O.sub.2   Moist O.sub.2                                        30         4 vials - total kill                                                                        9 vials - total kill                                 45         6 vials - total kill                                                                        10 vials - total kill                                60         8 vials - total kill                                                                        --                                                   75         10 vials - total kill                                                                       --                                                              Dry N.sub.2   Moist N.sub.2                                        30         0 vials - total kill                                                                        0 vials - total kill                                 45         0 vials - total kill                                                                        0 vials - total kill                                 60         1 vial - total kill                                                                         2 vials - total kill                                 75         2 vials - total kill                                                                        3 vials - total kill                                            Dry Ar        Moist Ar                                             30         0 vials - total kill                                                                        0 vials - total kill                                 45         0 vials - total kill                                                                        1 vial - total kill                                  60         1 vial - total kill                                                                         2 vials - total kill                                 75         2 vials - total kill                                                                        3 vials - total kill                                 ______________________________________                                    

EXAMPLE 19

With Pyrex chamber (9"D×13"L) and cooled internal metallic perforatedcylinder, (FIG. 1)

Gas: O₂

Flowrate: 100 scc/min

Pressure: 0.280 torr

RF Power Density: 0.020 W/cc

Exposure time: 70-105 min

Temperature: 50° C.

Samples:

a. 24-inch long PVC tubing with internal diameter of 11 mm and wallthickness of 2 mm.

b. 24-inch long silicone rubber tubing with internal diameter of 3/16"and wall thickness of 1/16".

Spore strip was placed in middle of tubing at approximately 18-inch fromeither free end of tubing. The latter was bent into a U-shape and placedwithin a Tyvek/polyethylene pouch and sealed prior to plasmasterilization.

Percent Kill: Total Kill

EXAMPLE 20

With Pyrex chamber (9"D×13"L) and cooled internal perforated metalliccylinder, (FIG. 1)

Gas: Dry and Moist Nitrogen-Oxygen and Argon-Oxygen Mixtures (O₂:5-15%); (H₂ O level: 300 ppm)

Flowrate: 100 scc/min

Pressure: 0.275-0.300 torr

RF Power Density: 0.020 W/cc

Temperature: 34°-53° C.

Sample Size per Experiment: Ten (10) 3M "Attest" vials with 4×10⁶spores/strip in each vial, placed in a sealed Tyvek/polyethylene pouch

    ______________________________________                                        Exposure                                                                      Time (min)                                                                    ______________________________________                                                    Dry N.sub.2 --O.sub.2                                                                      Moist N.sub.2 --O.sub.2                              30          1 vial - total kill                                                                        1 vial - total kill                                  45          1 vial - total kill                                                                        1 vial - total kill                                  60          2 vials - total kill                                                                       3 vials - total kill                                 75          3 vials - total kill                                                                       4 vials - total kill                                             Dry Ar--O.sub.2                                                                            Moist Ar--O.sub.2                                    30          1 vial - total kill                                                                        1 vial - total kill                                  45          1 vial - total kill                                                                        2 vials - total kill                                 60          3 vials - total kill                                                                       4 vials - total kill                                 75          4 vials - total kill                                                                       5 vials - total kill                                 ______________________________________                                    

I claim:
 1. A method for sterilization and treatment of medical anddental devices and materials comprising the steps of,placing saiddevices and materials within a first fluid cooled metallic perforatedelectrode, said electrode being positioned within, and spaced from agas-tight confining chamber, evacuating said chamber to a substantiallylow pressure and introducing a gas into said chamber, initiating anelectrical discharge in said gas within said chamber by application ofan RF voltage between said internal perforated electrode and across thechamber wall, creating a gas plasma accompanied by a substantiallyfield-free and glowless volume within the perforated electrodecontaining said devices and materials, whereby said devices andmaterials are contacted by a substantially electrically neutral activespecies at a temperature below that which would be detrimental to saiddevices and materials, maintaining said gas plasma for a controlledperiod of time, maintaining a flow of said gas through said chamber; andwithdrawing said devices and materials from said chamber.
 2. A method inaccordance with claim 1 wherein said gas-tight confining chamber isfluid cooled.
 3. A method in accordance with claim 1 wherein said gastight chamber is formed of metal and is connected to a point ofpotential reference.
 4. A method in accordance with claim 3 wherein saidgas-tight confining chamber is fluid cooled.
 5. A method forsterilization and treatment of medical and dental devices and materialscomprising the steps of,placing said devices and materials within afirst fluid cooled metallic perforated electrode, said electrode beingpositioned within and spaced from a gas-tight confining chamber, saidchamber enclosing a fluid cooled second perforated metallic electrodepositioned between and spaced apart from said gas-tight chamber and saidfirst perforated electrode, evacuating said chamber to a substantiallylow pressure and introducing a gas into said chamber, initiating anelectrical discharge in said gas within said chamber by application ofan RF voltage between said second perforated electrode are across saidchamber wall, creating a gas plasma accompanied by a substantiallyfield-free and glowless volume within said first perforated electrodecontaining said devices and materials, whereby said devices andmaterials are contacted by substantially electrically neutral activespecies at a temperature below that which would be detrimental to saiddevices and materials, maintaining said gas plasma for a controlledperiod of time, and maintaining a flow of said gas through said chamber;withdrawing said devices and material from said first perforatedelectrode.
 6. A method in accordance with claim 5 wherein said gas-tightconfining chamber is fluid cooled.
 7. A method in accordance with claim5 wherein said gas-tight chamber is formed of metal and is connected toa point of potential reference.
 8. A method in accordance with any oneof claims 1, 3, 5, 6, and 7 wherein said devices and materials areenclosed within sealed pouches formed of gas-permeable material whilesaid pouches containing said materials and devices are within saidchamber.
 9. A method in accordance, with any one of claims 1, 3, 5, 6,and 7 wherein said gas comprises one or more of the group of gasesconsisting of:hydrogen; oxygen; nitrogen; hydrogen-oxygen mixtures;hydrogen-oxygen-inert gas mixtures; oxygen-nitrogen mixtures;oxygen-nitrogen-inert gas mixtures; nitrogen-hydrogen mixtures;nitrogen-hydrogen-inert gas mixtures; oxygen-nitrogen-hydrogen mixtures;oxygen-nitrogen-hydrogen-inert gas mixtures; oxygen-helium mixtures;nitrogen-helium mixtures; hydrogen-helium mixtures; oxygen-organohalogenmixtures; oxygen-organohalogen-inert gas mixtures;oxygen-organohalogen-nitrogen mixtures; oxygen-inorganic halogenmixtures; oxygen-inorganic halogen-inert gas mixtures; oxygen-inorganichalogen-nitrogen mixtures; oxygen-inorganic oxyhalogenated compoundmixtures; oxygen-inorganic oxyhalogenated compound-inert gas mixtures;oxygen-inorganic oxyhalogenated compound-nitrogen mixtures, helium,argon, helium-argon mixtures.
 10. A method in accordance with any one ofclaims 1, 3, 5, 6, and 7 and wherein said gas comprises water vapor inexcess of 100 ppm as a constituent in a binary mixture with any one ofthe groups of gases consisting of oxygen, nitrogen, argon or a halogen.11. A method for sterilization and treatment of medical and dentaldevices and materials comprising the steps of,placing said devices andmaterials on a generally planar fluid cooled metallic electrode, saidelectrode being positioned within a gas-tight confining chamber, saidchamber being made of metal and connected to a point of potentialreference, the internal surface area of said chamber being substantiallylarger than the surface area of said planar electrode, further includinga perforated metallic enclosure within said chamber, said perforatedenclosure being insulated from, but surrounding and containing saidplanar electrode and said devices and materials positioned thereon, saidenclosure being connected to said point of potential reference, wherebysaid devices and materials are contacted by a substantially electricallyneutral active species at a temperature that which could be detrimentalto said devices and materials, evacuating said chamber to asubstantially low pressure and introducing a gas into said chamber,initiating an electrical discharge in said gas within said chamber byapplication of an RF voltage between said planar electrode and saidpoint of potential reference creating a gas plasma, maintaining said gasplasma for a controlled period of time, maintaining a flow of said gasthrough said chamber; and withdrawing said devices and materials fromsaid chamber.
 12. A method in accordance with claim 11 wherein saidgas-tight confining chamber is fluid cooled.
 13. A method in accordancewith either of claims 11 or 12 wherein said gas comprises one or more ofthe groups of gases consisting of:hydrogen; oxygen; nitrogen;hydrogen-oxygen mixtures; hydrogen-oxygen-inert gas mixtures;oxygen-nitrogen mixtures; oxygen-nitrogen-inert gas mixtures;nitrogen-hydrogen mixtures; nitrogen-hydrogen-inert gas mixtures;oxygen-nitrogen-hydrogen mixtures; oxygen-nitrogen-hydrogen-inert gasmixtures; oxygen-helium mixtures; nitrogen-helium mixtures;hydrogen-helium mixtures; oxygen-organohalogen mixtures;oxygen-organohalogen-inert gas mixtures; oxygen-organohalogen-nitrogenmixtures; oxygen-inorganic halogen mixtures; oxygen-inorganichalogen-inert gas mixtures; oxygen-inorganic halogen-nitrogen mixtures;oxygen-inorganic oxyhalogenated compound mixtures; oxygen-inorganicoxyhalogenated compound-inert gas mixtures; oxygen-inorganicoxyhalogenated compound-nitrogen mixtures, helium, argon, helium-argonmixtures.
 14. A method in accordance with either claims 11 or 13 whereinsaid medical devices and materials are enclosed within pouches made ofpermeable material.
 15. A method in accordance with either of claims 11or 13 wherein said gas comprises water vapor in excess of 100 ppm in abinary mixture with any one of the groups of gases consisting of oxygen,nitrogen, argon or a halogen.
 16. A method for sterilization andtreatment of narrow bore, elongated and generally tubular devicescomprising the steps of,placing a said device within a generallycylindrical, narrow, elongated gas-tight confining chamber, said chamberhaving an inside diameter at least one and one half times that of theouter diameter of said elongated device, said chamber being plugged atboth ends with gas permeable membranes, said membranes being imperviousto microorganisms, said plugged chamber being removably connectedthrough said membranes to a gas delivery system at one end thereof andto a gas exhaust system at the other end thereof, evacuating saidchamber through said gas exhaust system to a substantially low pressureand introducing a gas from said gas delivery system into said chamber,initiating an electrical discharge in said gas within said chamber byapplication of a high frequency electromagnetic field in close proximityto said chamber, creating a gas plasma within said chamber, whereby saidelongated device is contacted by plasma active species along its entireouter and inner surfaces at a temperature below that which would bedetrimental to said device, maintaining said gas plasma for a controlledperiod of time, maintaining a flow of said gas through said chamber,disconnecting said chamber from said gas delivery and exhaust systems,without removal of said membranes from said chamber and withdrawing saidchamber from said proximity of said electromagnetic field, and storingsaid device within said membrane-sealed chamber.
 17. A method inaccordance with claim 16 wherein said gas-tight confining chamber isfluid cooled.
 18. A method in accordance with claim 16 wherein said gascomprises one or more of the group of gases consisting of:hydrogen;oxygen; nitrogen; hydrogen-oxygen mixtures; hydrogen-oxygen-inert gasmixtures; oxygen-nitrogen mixtures; oxygen-nitrogen-inert gas mixtures;nitrogen-hydrogen mixtures; nitrogen-hydrogen-inert gas mixtures;oxygen-nitrogen-hydrogen mixtures; oxygen-nitrogen-hydrogen-inert gasmixtures; oxygen-helium mixtures; nitrogen-helium mixtures;hydrogen-helium mixtures; oxygen-organohalogen mixtures;oxygen-organohalogen-inert gas mixtures; oxygen-organohalogen-nitrogenmixtures; oxygen-inorganic halogen mixtures; oxygen-inorganichalogen-inert gas mixtures; oxygen-inorganic halogen-nitrogen mixtures;oxygen-inorganic oxyhalogenated compound mixtures; oxygen-inorganicoxyhalogenated compound-inert gas mixtures; oxygen-inorganicoxyhalogenated compound-nitrogen mixtures, helium, argon, helium-argonmixtures.
 19. A method in accordance with claim 16, wherein said gascomprises a binary mixture of water vapor in excess of 100 ppm as aconstituent and one of the group of gases consisting of oxygen,nitrogen, argon or a halogen.
 20. A method in accordance with any one ofclaims 16, 18 or 19 wherein said devices are enclosed withingas-permeable sealed pouches during processing.